How is it worth it to slow down your code development to write tests? Won't it take you a long time to learn how to write tests? Won't it take longer if you have to write tests AND develop new features, fix bugs? Isn't it hard to write test code? To maintain test code? We will address these questions as we talk about how test code is crucial for our software. By way of illustration, we will show how it has played a vital role in making Blacklight a true community collaboration, as well as how it has positively impacted coding projects in the Stanford Libraries.